A wide variety of lesions, including internal hemorrhoids, polyps, and mucositis, may be treated by severing snare ligation.
In severing snare ligation, a targeted lesion is removed from the surrounding tissue by an electrosurgical severing snare using radio frequency (R/F) electric current to sever tissue or to achieve hemostasis. A high radio frequency is used (i.e., above 100,000 Hz.) to avoid the potentially injurious stimulation of muscles and nerves which results from lower frequency R/F energy. Thus, electrosurgery is typically performed at frequencies of approximately 500,000 Hz., although frequencies as high as 4,000,000 Hz. may be used.
Medical diathermy is similar to electrosurgery in that radio frequency current is passed through the patient's body. The major difference between these two techniques is the density of the radio frequency electric current; the current density used in medical diathermy is kept low to reduce tissue heating and to prevent necrosis.
There are three surgical effects that can be achieved with electrosurgery. These include electrosurgical desiccation, which is a low power coagulation caused without sparking to the tissue; electrosurgical cutting, where electricity sparks to the targeted tissue and produces a cutting effect; and electrosurgical fulguration, where electricity sparks to the targeted tissue without causing significant cutting.
The above-described surgical effects can be accomplished by using either a monopolar or bipolar output. For many applications, however, bipolar outputs are preferable because the patient return electrode (necessary in monopolar procedures and a common source of accidents) is eliminated, and any desiccation performed is extremely localized because, in a true bipolar operation, only the tissue that is grasped between the two electrodes is desiccated. Bipolar output, however, is less effective for cutting and fulgurating, and thus monopolar tools remain commonplace. Severing snares, for example, are almost all monopolar instruments.
In addition, three types of electrical current waveforms are typically used in electrosurgery. These include a "cutting" waveform, which cuts tissue very cleanly but may cause the incised tissue to bleed excessively; a "coagulating" waveform, which desiccates and fulgurates tissue without significant cutting; and a "blended" waveform, which is a cutting waveform that has a moderate hemostatic effect. A waveform's "Crest Factor" describes the degree of hemostasis that a waveform will produce if properly applied.
To remove a lesion (or polyp) with an electrosurgical severing snare, the wire snare is looped around the targeted lesion and is tightened as the snare is drawn into the sheath. The lesion is then desiccated and cut through electrosurgically. It is also possible to sever a lesion in a single step by cutting with a "blended" current. This allows a snare to cut through a lesion in one pass without having to worry about bleeding. Alternately, the lesion may be cut through mechanically with a thin snare wire after the blood supply to the targeted tissue has been coagulated and the tissue has been softened by a desiccation current.
Saline-Assisted Polypectomy (SAP), or "strip biopsy," has become an increasingly popular way of performing endoscopic mucosal resection (EMR) to diagnose and treat diseases of the gastrointestinal tract. When performing SAP, a surgeon passes a needle through an endoscope and inserts the needle into the submucosa layer proximate to the lesion. Next, the surgeon injects physiological saline into the submucosa to elevate the lesion on a bed of saline solution. Once elevated, the surgeon can easily remove the lesion by passing an electrosurgical severing snare over the lesion and ligating the lesion. SAP, however, typically requires the use of a large diameter double-channel endoscope, which is difficult to introduce into the patient and is hard to manipulate. In addition, grasping forceps must be used to lift the lesion off of the layer of saline solution, which may result in a tear in the mucosa.
Accordingly, an alternate procedure has been developed called endoscopic aspiration mucosectomy (EAM). As described by Torii et al. in "Endoscopic Aspiration Mucosectomy as Curative Endoscopic Surgery," Gastrointestinal Endoscopy, Vol. 42, No. 5 (1995), EAM can be used to lift up a targeted lesion with suction, rather than with forceps, thereby reducing the risk of injury to the mucosal surface. When performing EAM, a double-channel endoscope is introduced into the patient, the lesion is marked with a needle knife, and saline solution or Glyceol.TM. (e.g., a hypertonic solution of 10% glycerol, 5% fructose, and physiological saline solution; available from Chugai Pharmaceutical Co., Tokyo, Japan) is injected into the submucosal layer beneath the lesion to separate the lesion from the layer. Next, the double-channel endoscope is withdrawn from the patient and a single-channel, video endoscope equipped with a transparent aspiration cylinder is introduced into the patient and (e.g., a Teflon.RTM. tube through which suction is applied) an electrosurgical severing snare is tightened around the outer circumference of the cylinder.
Once the single-channel endoscope has been properly repositioned near the targeted lesion, the lesion and the surrounding mucosa are aspirated into the cylinder and the snare is pushed off the cylinder and tightened around the lesion to ligate the lesion. By first aspirating the lesion into the tube before severing it, the lesion may be severed further down on the stalk than possible with SAP. After the targeted lesion has been severed from the surrounding tissue, the severed tissue may remain aspirated into the cylinder to retrieve the sample for further study. Alternately, the severed tissue may be aspirated out of the cylinder to pass through the body naturally.
However, while the EAM procedure described by Torii et al. may offer certain advantages over SAP, it still has its disadvantages. To perform EAM, a surgeon must switch between a double-channel endoscope having a needle knife and an injection needle (for marking the lesion and injecting solution), and a more maneuverable single-channel endoscope having a severing snare and an aspiration cylinder(for ligating and aspirating the lesion) because the working channel of a single-channel endoscope cannot accommodate both an injection needle and a severing snare simultaneously. Alternately, as discussed by Torii et al., double-channel endoscopes are too large and are not desirable for the EAM procedure. Exchanging endoscopes, however, is time consuming-wasting surgeons' time and prolonging the procedure.
U.S. Pat. No. 5,542,948 to Weaver et al. purports to disclose an instrument in which a severing snare and an injection needle disposed side-by-side in separate lumens of the device are prevented from being simultaneously deployed by an actuator assembly which maintains one of the instruments (e.g., the severing snare) within the lumen until the other instrument (e.g., the injection needle) has been completely withdrawn into its respective lumen.
This requires the use of a multi-lumen sheath including two lumens for carrying the injection needle and severing snare. However, multi-lumen sheaths take up valuable space and make the overall endoscopic apparatus large and bulky. The use of two lumens within a sheath also limits the size of the severing snare and injection needle that can be used, as the instruments are disposed through the sheath side-by-side.
In addition, the depth at which a surgeon using the apparatus disclosed by Weaver et al. may sever a lesion is limited because the device is designed to be used when performing SAP and does not, therefore, provide for an aspirating device. This prevents the use of the device of Weaver et al. in performing EAM.